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In calcium phosphate, $\ce{Ca3(PO4)2}$, since the calcium and phosphate share an ionic bond, and the phosphorus and oxygen share a covalent bond, should the Lewis structure be like the following?
While I was checking other web pages I noticed there was another Lewis structure for the same molecule:
Are they both possible Lewis structures, or is the first structure the only "correct" version of the molecule?
Calcium phosphate crystallises in a number of different modifications of which β-$\ce{Ca3(PO4)2}$ is the stable room temperature and ambient pressure modification. It has a rather complex structure not easily described, consisting of chains and rings with phosphate and calcium ions in specific patterns. It is orthorhombic, but $c \gg b \approx a$.
Any attempt to simplify its structure by drawing it in pseudocovalent depictions like your lower scheme is doomed to fail. Better just use the upper scheme; unless you are expected to know a certain salt’s crystal structure that one is safe.
